The present invention is concerned in general with interchangeable cutting tool inserts and more particularly with the chip breaker grooves in such interchangeable inserts.
Chip breaking grooves have been known and used in the tool machine art for many years to assure that the chips are broken before they become long enough to become entangled in the tools, to damage the workpiece or to harm the operators. A class of grooves essentially shape the chips to add rigidity and therefore are more susceptible to breaking. Some of the grooves form the chips into spirals and the spirals break of their own weight before becoming large enough to cause damage. Other grooves both rigidize the chips as they are formed and direct the chips toward obstacles, such as the body of the tool holder which breaks the rigidized chip, thereby, preventing the chip from causing damage.
Over the years, variations of chip breaking grooves have been used to improve the chip breaking quality of the cutting tool insert. There are various criteria to determine whether chip breaking is being expenditiously accomplished. Among these criteria are:
(1) the size and the shape of the chips generated during the cutting operation; PA1 (2) the variation in feed rate that can be accomplished using the insert with the particular chip breaking groove; PA1 (3) the variation in the depth of the cut that can be accomplished using the insert with the particular chip breaking groove; PA1 (4) the power usage while using the insert with the particular chip breaking groove; and PA1 (5) the longevity of the inserts with the particular chip breaking groove.
Accordingly, ideally chip breaking grooves must generate chips that break while short, and are effective over a wide range of feed rates and depths and with a minimum of power usage. At the same time the chip breaker groove must not significantly decrease the life of the insert. Thus, there is a constant attempt to provide cutting inserts with chip breaking grooves which enable, for example, the use of the inserts for a wide assortment of feed rates and cutting depths. At the same time the designers of the inserts have attempted to decrease the forces, such as cutting forces or friction forces exerted between the chip and the insert to both prolong the life of the insert and to minimize the power used in the actual formation and breaking of the chips.
For example, U.S. Pat. No. 3,187,406 provides an insert with a continuous chip control groove which has dual tandem radii with the back radius of the groove being greater than the forward radius. The chip controlling groove of the patent has a constant cross-sectional shape and is spaced equidistant from the cutting edges throughout its circumferential length. The patent points out how the dual radii enables the same insert to be used when the feed rate is classified as light, medium or heavy. Thus the patent teaches controlling the chip by using as the first radius for a thin chip the second radius for a thicker chip and the area behind the inward side of the second radius for controlling and stressing the heavy or thick chips. However, most of the chip shaping occurs far removed from the cutting edge and therefore an inordinate amount of power is required to shape the chip.
The prior art such as shown in U.S. Pat. Nos. 3,187,406, 3,383,748 and 3,399,442 use chip control grooves to increase the rigidity of the ribbon separated from the workpiece by curling it along the back wall of the groove or by using a curved cutting edge to create a metal strip hving an appropriate shaped profile such that when it undergoes forced bending by an obstacle in its flowpath, stresses are created in the ribbon which cause it to break. The added rigidity of the shaped profile enables the breaking of the chips even though the radii of curvature is relatively great as compared with the thickness of ribbon.
The radii of curvature of the prior art formed chips is mainly influenced by the geometry of the chip control groove. Therefore, grooves having fixed shapes can control only a limited range of radii of curvature in chips. The variations in the dimensions and configuration of the chip control grooves of the prior art have only extended the range of feed rate and cutting depth to a very limited degree. In addition it is well known that minimizing contacts between the cut ribbon and the surface of the cutting insert minimizes the power consumed during the cutting operation.
The range of feed rates and depths for a given insert with chip breaking grooves has been augmented in the past by also varying the shape of the cutting edge to shape the strip. Varying the shape of the cutting edge to shape the strip, as noted hereinbefore, has significant drawbacks among which are the cut marks left on the workpiece when the cutting edge is not a straight line.
The creation of a profile in the cross-section of the chip can be obtained by various cutting insert configurations such as, for example, the configurations described in U.S. Pat. No. 3,815,191 and U.S. Pat. No. 4,140,431. The characteristic feature of the inserts and more particularly the chip forming portions of the insert of prior patents is that the form of the cross-section of the chip is obtained by breaking the continuity of the cutting edge. U.S. Pat. No. 3,815,192 shows another approach for obtaining a profile in the cross-sectional shape of the chip. That approach is to create the profile as chip exits from the chip control groove. The disadvantage of that approach is that the deformation in the chip occurs in a region where the temperature of the chip is relatively low and accordingly much greater power has to be expended in deforming the chip.
Accordingly it is an object of the present invention to provide new and improved cutting inserts with chip control grooves in which the above referred to disadvantages are substantially reduced or overcome. According to the present invention a chip breaker arrangement is provided comprising polygonal cutting inserts having top and bottom surfaces spaced apart from each other,
side surfaces joining and located between said top and bottom surfaces,
a cutting edge forming a straight line at the junction of the side surfaces and said top and bottom surfaces,
chip breaker means adjacent to said cutting edges in at least one of said top and bottom surfaces,
said chip breaker means comprising groove means,
cutting edge land means separating said groove means from said cutting edges, and
said chip breaker means having a plurality of variations along said cutting edges.